The use of glass bandings to hold the component parts of dynamoelectric machine armatures, armature windings and commutators in radial compression is well-known. Typically, such bandings are formed of glass tapes which are impregnated with a thermally curable bonding resin that helps lock the individual filaments of the banding tapes in fixed position within the bandings when the resin is cured. One example of such a thermosetting resin for a glass armature banding is described in U.S. Pat. No. 3,047,756 which issued on July 31, 1962 and is assigned to the assignee of the present invention. As is more fully explained in that patent, in the absence of a suitable bonding resin, the filaments of an armature banding tape would be subjected sequentially to the full tension forces applied to the tape, either one at a time or in small groups of filaments. Under such circumstances the individual filaments would tend to be easily broken thus causing the tape to become completely ruptured. In an attempt to eliminate this problem, it has become an accepted practice to form glass bandings on dynamoelectric machines by pre-stressing or tensioning the bandings as they are applied, then thermally curing the resin impregnated therein in an attempt to lock the individual filaments in a pre-stressed condition that will result in a more uniform sharing of the tension loads placed on the filaments during normal operation of the machine.
While such prior art banding techniques have been reasonably successful, they tend to suffer from two fundamental problems relatively frequently. The basic problem with such thermally cured bandings is that the bonding resins used therein tend to flow during the thermal curing process. This flowing of the bonding resins causes a relaxation of the pre-stress tension and so requires that additional layers of tape be applied in order to obtain the strength necessary for a given application. Of course, there are undesirable added expenses for materials and labor associated with the installation of such additional layers of banding tapes. A second fundamental problem with such prior art glass bandings and banding methods is that the high pre-stressing tensions often used in an attempt to counteract the inevitable relaxation inherent in the flow problem mentioned above sometimes produces a "starved" or dry band. Such a dry band results when too much resin is squeezed from between adjacent layers of a banding tape as it is wound, i.e., before an oven curing operation is performed on the resin to lock it in place relative to the layers of banding tape. Dry bands also are easily ruptured because individual filaments of the tape are free to shift sufficiently to cause them to assume a disproportionate share of the pre-tension loading, which snaps the filaments sequentially.
It would be desirable to provide a glass banding that does not possess the disadvantages potentially inherent in such presently known thermally cured glass bandings. Also, it would be desirable to provide a simplified method for installing glass bandings that would not require the use of large ovens for thermally curing the bandings after they are wound in their installed positions. In particular, it would be very desirable to provide a method for making glass bandings that would enable the bandings to be installed on a dynamoelectric machine while it is mounted on its normal bearings in the machine housing, rather than requiring the disassembly and transportation of the machine to a facility having a curing oven large enough to accommodate the armature and an auxiliary bearing support in order to thermally cure a glass banding wound thereon. While such large furnaces are normally available at manufacturing sites where dynamoelectric machines are initially fabricated, it is often necessary to replace glass bandings on such machines after they have been placed in use, thus, it is often very inconvenient and expensive to be forced to utilize a banding method that requires the use of such a large oven. In fact, at the present time, to effect re-banding of large dynamoelectric machines, it is usually necessary to remove the machines from service and transport them to a large oven in which new thermally-curable glass bandings can be appropriately treated and cured after they are wound in place on the machines.
In addition to the use of heat curable resins on glass armature bandings, in a manner that requires a resin to be cured in place after it has been wound under a suitable pre-stress tension on the armature, it is generally known in the prior art to use ultraviolet or irradiation curable resin materials to form webbings of a type that might be suitable for use in glass banding of armatures, as well as to form protective coatings on various types of electric products. In this regard, U.S. Pat. No. 3,878,019, which issued on Apr. 15, 1975, discloses a process of producing spot bonded non-woven webs by applying a film-forming polymer to web filaments and subsequently cross-linking the polymer by photochemical means. An example of an electrical product that is manufactured by using an irradiation process to cure a resin therein is disclosed in U.S. Pat. No. 2,793,970, which issued on Mar. 29, 1957 and describes a process for making electrical capacitors. In the process taught by this patent, a plurality of sheet electrodes are spaced apart by solid dielectric material in a tank filled with a liquid dielectric chosen from a group of organic monomers which polymerize upon irradiation. These components are contained in a suitable capacitor tank that is subjected to ionizing radiation by rotating the contents of the tank to uniformly expose them to an irradiating beam that is sufficient to cure and solidify the liquid dielectric between the spaced sheet electrodes. A somewhat similar process is shown in U.S. Pat. No. 3,924,022 which issued on Dec. 2, 1975 and is assigned to the assignee of the present invention. In that patent there is described a method for applying an organic coating to a steel sheet that is useful for making laminated products, such as the cores of electrical power transformers. In the process described in the patent, a strip of magnetically oriented steel is first treated with an irradiation curable organic resin to a thickness of up to 2 mils. The treated steel strip is then passed through an irradiation curing zone to effect a cure of the organic resin to a suitable hardness.
Finally, it is generally known to use a variety of different methods for irradiation curing various resins to form hardened coatings. For example, U.S. Pat. No. 3,531,317 which issued on Sept. 29, 1970, explains a process for hardening polyester molding and coating masses by subjecting them to electron radiation. The use of an irradiation-sensitive catalyst precursor to control polymerization of epoxide monomers and prepolymers is described in U.S. Pat. No. 3,721,617 which issued on Mar. 20, 1973. Another patent, U.S. Pat. No. 3,770,490 which issued on Nov. 6, 1973 generally describes a method for curing acrylic syrups that are useful as interior coatings for containers. The method described in that patent utilizes either ionizing irradiation or atomic light to cure the acrylic syrups described therein.